Dehydroepiandrosterone 7alpha- and 7beta-hydroxylation in mouse brain microsomes. Effects of cytochrome P450 inhibitors and structure-specific inhibition by steroid hormones.
Presently, several works question the effects of dehydroepiandrosterone (DHEA) reported in vivo and designate its 7-hydroxylated metabolites as native antiglucocorticoids and potent mediators in the triggering of immune response. Among mouse tissues and organs, and second to liver, the largest production of 7alpha-and 7beta-hydroxylated derivatives of DHEA takes place in brain microsomes. To contribute to identification of cytochromes P450 (CYPs) responsible for 7alpha- and 7beta-hydroxy-DHEA production, effects of CYP inhibitors and of several steroid hormones on DHEA 7-hydroxylation were examined. Using mouse brain microsomes as a source of enzyme, we report now that strong and smaller inhibitions of DHEA 7alpha-hydroxylation were obtained with ketoconazole and alpha-naphthoflavone, respectively, and that neither changed DHEA 7beta-hydroxylation. Metyrapone and antipyrine also inhibited 7alpha-hydroxylation, but by contrast, significantly increased 7beta-hydroxylation of DHEA. This indicated that at least, two different CYPs were responsible for 7alpha- and 7beta-hydroxylation of DHEA. Steroids sharing a 3beta-hydroxylated structure with DHEA, namely pregnenolone, 5-androstene-3beta,17beta-diol and 3beta-hydroxy-5alpha-androstan-17-one, were strong inhibitors of DHEA 7alpha-hydroxylation (non-competitive inhibition with pregnenolone, Ki=2.0 +/- 0.3 microM). In contrast, 7beta-hydroxylation yields were not decreased by the 3beta-hydroxysteroids tested. Moderate inhibition of 7alpha- and 7beta-hydroxylation was obtained with 3-oxosteroids, namely testosterone, progesterone, corticosterone and 4-androsten-3,17-dione. Taken together, these data indicate specific inhibition patterns of DHEA 7alpha- and 7beta-hydroxylation by CYP inhibitors and steroid hormones in mouse brain microsomes and may be used as criteria necessary for identification of the responsible CYP species.
Doostzadeh
J
J
Laboratoire de Biotechnologie, Conservatoire national des arts et métiers, Paris, France.
Cotillon
A C
AC
Morfin
R
R
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D003687:Dehydroepiandrosterone / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006728:Hormones / Q000494:pharmacology*; D006900:Hydroxylation; D007700:Kinetics; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism; D013256:Steroids / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D006728:Hormones; D013256:Steroids; D003687:Dehydroepiandrosterone; D003577:Cytochrome P-450 Enzyme System